250K miles on my '05 TJR, I never shift the transfer case stopped I often shift it at highway speeds as the dry pavement transitions to ice, slush or compact snow. Same with my YJ which I drove for 20 years and 330K miles. I now have a n '06 TJR with under 60K miles and it likely never saw 4WD used, there is zero difference in how the '05, '06 feel when shifting in or out of 4H. Clutch in is always a good idea.
The theory is flawed. Yes, both axles must be turning identical speeds, yes you should shift travelling in a straight line and yes you should lift off the throttle so there wull be no tires slipping. But in a straight line, power off there is no wear even at 70mph even on dry pavement.
We are also talking about vehicles like Wranglers with the same front and rear axle ratios. Old school pickups often had different front and rear ratios. F250s, I've had 3, all came with 4.10 Dana 44 front axles 41/10, and 4.11 Dana 60 rear axles, 35/9. Those shifted into 4WD best at 15mph. And they only shifted out of 4WD after reversing for 15'. Pretty sure GM and Dodge did the same thing back then. The speed difference kept a tension in the power train rliminating any play or slack. If you pulled onto dry pavement in 4WD you would hear a howl from the transfer case.
I change transfer case oil every 2 or 3 years, I've never seen these chips of metal you speak of.